AIDS is a major public health problem worldwide. Although drugs targeting HIV viruses are in wide use and have shown effectiveness, toxicity and development of resistant strains have limited their usefulness. Assay methods capable of determining the presence, absence or amounts of HIV viruses are of practical utility in the search for inhibitors as well as for diagnosing the presence of HIV.
A conventional process for preparation of a HIV protease inhibitor (PI) of Formula I
is lengthy, affords a low yield of approximately 1%, is variably reproducible, requiring numerous chromatographic purification steps, and employs undesirable reagents, such as ozone, sodium cyanoborohydride, and tributyltin hydride. The compound of Formula I is an HIV protease inhibitor which has been made and disclosed in WO2003/090690.
Methods for the preparation of the bisfuran alcohol intermediate used in the synthesis of the compound of formula I have been described by Pezechk (Pezechk, M. et al., Tetrahedron Letters, 1986, 27, 3715.) and Ghosh (Ghosh, A. K. et al., J. Med. Chem., 1994, 37, 2506; Ghosh A. K. et al., J. Med. Chem., 1996, 39, 3278; Ghosh, A. K. et al., Tetrahedron Letters, 1995, 36, 505).
Scheme 1 shows the bisfuran alcohol synthesis from Ghosh, A. K. et al., Tetrahedron Letters, 1995, 36, 505).

Conventional methods require multiple steps and the use of toxic reagents. In one of the methods (Ghosh, A. K. et al., Tetrahedron Letters, 1995, 36, 505), resolution of a racemic mixture was achieved by exposure to an immobilized enzyme followed by chromatographic separation.

Reactive carbonate esters have been prepared from bisfuran alcohol (1) and dipyridyl carbonate (Ghosh A. K. et al., J. Med. Chem., 1996, 39, 3278), and p-nitrophenol chloroformate (X. Chen et al., Bioorganic and Medicinal Chemistry Letters, 1996, 6, 2847). These reagents couple with nucleophilic reaction partners, but do not always display the appropriate reactivity and efficiency.

Methods exist for the preparation of chiral haloalcohols derived from N=protected amino acids (Albeck, A. et al., Tetrahedron, 1994, 50, 6333). Methods for the conversion of such chloroalcohols to carbamate sulfonamide derivatives are known (Malik, A. et al., WO 01/46120A1). The halohydrins can also be converted to epoxides and converted to carbamate sulfonamide derivatives in a similar manner (WO 03/090690).
Preparation of carbamate derivatives of aminophosphonic acids and subsequent conversion to phosphonate mono- and diesters have been described in Yamauchi, K. et al., J. Org. Chem., 1984, 49, 1158; Yamauchi, K. et al., J. Chem. Soc. Perkin Trans. I, 1986, 765.
Aminoethyl phosphonate diesters can be prepared by a process involving acylation of an amino phosphonic acid with acyl halides or benzyl chloroformate (CBZCl) to form compounds of Formula VII

Compounds of Formula VII can be activated and condensed with phenol to form a compound of Formula VIII

A compound of Formula VIII can be activated and condensed with a second alcohol or phenol to form IX

A compound of Formula IX can be deacylated to form an amino phosphonate compound of Formula X

A compound of Formula X can be isolated as a salt of an organic or inorganic acid.
The Ghosh process for bisfuran alcohol (Ghosh, A. K. et al, J. Org. Chem., 1995, 36, 505) requires the use of tributyltin hydride and ozone.
The free base of a compound of Formula I is non-crystalline and hygroscopic with limited stability in protic solvents.
Thus, there exists a need to develop syntheses of more stable forms of the PI of Formula I. There also exists a need to develop more efficient processes of synthesizing the PI of Formula I.